Overview of MDM Metadata Objects in the OLAP API

The OLAP API implementation of the MDM model is represented by classes in the oracle.express.mdm package. Most of the classes in this package implement metadata objects, such as dimensions and measures. The following diagram introduces the subclasses of the MdmObject class.

Figure 2-1 MdmObject Class and Its Subclasses.

Text description of the illustration mdobject.gif

Mapping of OLAP Metadata Objects to MDM objects

An application accesses metadata objects by creating an OLAP API MdmMetadataProvider and using it to discover the available metadata objects in the data store.

The metadata objects that a database administrator specifies using the OLAP Metadata APIs map directly to MDM metadata objects that are accessible through the MdmMetadataProvider. The following table presents the typical mapping.

OLAP Metadata Objects	MDM Metadata Objects
Dimension	MdmHierarchy or MdmListDimension
Hierarchy	MdmHierarchy
Level	MdmLevel
Measure	MdmMeasure
Attribute	MdmAttribute
Measure Folder	MdmSchema

This chapter describes the MDM metadata objects. For information about how an application discovers the available MDM metadata objects in the data store, see Chapter 4, "Discovering the Available Metadata".

MdmSchema and MdmSource are the two subclasses of MdmObject.

MdmSchema Class

An MdmSchema represents a set of data that is used for navigational purposes. An MdmSchema is a container for MdmMeasure, MdmDimension, and other MdmSchema objects. An MdmSchema is equivalent to a folder or directory that contains associated items. It does not correspond to a relational schema in the Oracle database. Instead, it corresponds to a measure folder, which can include data from several relational schemas and which was created by a database administrator using the OLAP Metadata APIs.

Data that is accessible through the OLAP API is arranged under a top-level MdmSchema, which is referred to as the root MdmSchema. Under the root, there are one or more subschemas. To begin navigating the metadata, an application calls the getRootSchema method on the MdmMetadataProvider, as explained in Chapter 2, "Understanding OLAP API Metadata".

The root MdmSchema contains all the MdmDimension objects that are in the data store. Most MdmDimension objects are contained in subschemas under the root MdmSchema. However, a data store can contain a dimension that is not included in a subschema. The root MdmSchema contains MdmDimension objects that are in subschemas as well as MdmDimension objects that are not.

The root MdmSchema contains MdmMeasure objects only if they are not contained in a subschema. Because most MdmMeasure objects belong to a subschema, the root MdmSchema typically has no MdmMeasure objects.

An MdmSchema has methods for getting all the MdmMeasure, MdmDimension, and MdmSchema objects that it contains. The root MdmSchema also has a method for getting the measure MdmDimension, whose elements are all the MdmMeasure objects in the data store regardless of whether they belong to a subschema.

MdmSource Class

An MdmSource represents a measure, dimension, or other set of data (such as an attribute) that is used for analysis. This abstract class is the basis for some important MDM metadata classes, such as MdmMeasure, MdmDimension, and MdmAttribute.

MdmSource objects represent data, but they do not provide the ability to create queries on that data. Their function is informational, recording the existence, structure, and characteristics of the data. They do not give access to the data values.

In order to access the data values for a given MdmSource, an application calls the getSource method on the MdmSource. This method returns a Source through which an application can create queries on the data represented by the MdmSource. The following line of code creates a Source from an MdmDimension called mdmProductsDim.

Source productsDim = mdmProductsDim.getSource();

A Source that is the result of the getSource method on an MdmSource is called a primary Source. An application creates new Source objects from this primary Source as it selects, calculates, and otherwise manipulates the data. Each new Source specifies a new query.

For more information about working with Source objects, see Chapter 5, "Introduction to Querying".

The rest of this chapter describes the subclasses of MdmSource, along with other classes, such as MdmDimensionDefinition and MdmDimensionMemberType, that are closely related.